Much has been written about the influence of immigration on the history of the United States, and about the ways in which successive waves of immigrants, driven by domestic and foreign economic forces and often confronted by religious and social prejudices, have shaped our population and its culture. Little has been said, however, about the ways in which medical knowledge and public health practices, evolving over time and interacting with socioeconomic trends, have contributed to the total process by which newcomers are assimilated into the population.